1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device and, in particular, to a technique to remove a residue generated during a heating process.
2. Description of the Related Art
In recent years, structures of semiconductor devices such as an acceleration sensor have become increasingly finer, and thus contamination of the semiconductor wafer by fine particles or trace amount of metal directly affects the reliability and production yield of the semiconductor devices. Therefore, cleaning of the semiconductor wafer is one of the critical steps in manufacturing the semiconductor devices.
There are various approaches to clean the semiconductor wafer which depends on the types of contamination of the semiconductor wafer. For instance, in order to remove an organic material, an oxidizing acid such as H2SO4 is used, whereas in order to remove an oxidized film residue and a native-oxidized film, aqueous hydrogen fluoride (HF) is used. In order to remove contaminants including particles and metallic impurities, a so-called RCA cleaning method has been proposed by W. Kern and D. A. Puotinen in RCA Review, vol. 31, pp. 187, 1970 which uses a first solution (SC1) including aqueous ammonia solution (NH4OH) and hydrogen peroxide solution (H2O2) and a second solution (SC2) including hydrochloric acid (HCl) and hydrogen peroxide solution. In this case, SC1 is effective for removing the particles and SC2 is effective for removing the metallic impurities.
After the above described cleaning process, a drying process of the semiconductor wafer is performed. Among various drying techniques, a spin drying process is the most common technique. This technique however has several drawbacks such as generation of dust from a spin drying apparatus, buildup of an electrostatic charge due to high-speed rotation of the apparatus, and generation of a stain called a ‘watermark’ on a surface of the semiconductor wafer. In the case of a small-scale acceleration sensor having a plurality of fine openings, the clearance between a movable center weight and a proximal section therefrom is merely an order of several microns. Therefore, a drying process using a temperature-controlled bath may cause an operation problem due to sticking of the center weight and the proximal section.
In order to avoid these problems, several approaches have been proposed, such as drying the semiconductor wafer by using an isopropyl alcohol vapor or drying the semiconductor wafer by vertically drawing up the semiconductor wafer, so that the semiconductor wafer passes through an interface between isopropyl alcohol and pure water.
In Japanese Patent Application Kokai (Laid open) No. H9-069509, another drying technique is disclosed which has the steps of, after cleaning the semiconductor wafer by pure water, spraying isopropyl alcohol vapor onto a surface of the semiconductor wafer in order to absorb moisture on the surface of the semiconductor wafer, and then drying the semiconductor wafer at a temperature of 100° C. while blowing nitrogen onto the semiconductor wafer. The drying technique of Japanese Patent Application Kokai No. H9-069509 thus remarkably reduces generation of stains because the surface of the semiconductor wafer is dried under the nitrogen atmosphere.
However, the drying of the semiconductor wafer by using the isopropyl alcohol vapor may generate a residue of the isopropyl alcohol vapor on the surface of the semiconductor wafer. It has been found that an additional cleaning step after drying the semiconductor wafer under the isopropyl alcohol vapor atmosphere may cause a reaction between the residue of isopropyl alcohol vapor, cleaning solution and a conducting layer formed on the semiconductor wafer. This reaction leads to a problem of dissolution of the conducting layer. Specifically, it has been found that a reaction between the residue of isopropyl alcohol vapor, fuming nitric acid and an aluminum or aluminum alloy (Al—Si—Cu) conducting layer dissolves the conducting layer. Dissolution of the conducting layer may deteriorate characteristics of the semiconductor device and may lead to an operation problem of the semiconductor device.